1. Field of the Invention
The present invention relates generally to a cellular radio communication system, and more particularly, to a method in which a transmitter informs a receiver of a reference signal pattern that is to be muted in a system.
2. Description of the Related Art
Mobile communication systems have evolved into high-speed, high-quality wireless packet data communication systems that provide data services and multimedia services that far exceed the early voice-oriented services. Various mobile communication standards have been developed to support services of the high-speed, high-quality wireless packet data communication systems. These standards include High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), both defined in 3rd Generation Partnership Project (3GPP), High Rate Packet Data (HRPD) defined in 3rd Generation Partnership Project-2 (3GPP2), and 802.16 defined in Institute of Electrical and Electronic Engineers (IEEE).
The existing 3rd generation wireless packet data communication systems, such as HSDPA, HSUPA and HRPD, use specific technologies, such as an Adaptive Modulation and Coding (AMC) method and a Channel-Sensitive Scheduling (CSS) method, to improve transmission efficiency. Through the use of the AMC method, a transmitter can adjust an amount of transmission data according to a channel state. Specifically, when the channel state is not ‘Good’, the transmitter reduces the amount of transmission data to adjust a reception error probability to a desired level. When the channel state is ‘Good’, the transmitter increases the amount of transmission data to adjust the reception error probability to the desired level, thereby efficiently transmitting a large volume of information. Through the use of a CSS-based resource management method, the transmitter selectively services a user having a channel state that is better than those of other users. This selective servicing provides an increase in system capacity when compared to a method of allocating a channel to one user and servicing the user with the allocated channel. Such a capacity increase is referred to as ‘multi-user diversity gain’. Thus, the AMC method and the CSS method each apply an appropriate modulation and coding scheme at the most-efficient time, which is determined based on partial channel state information that is fed back from a receiver.
Research has been conducted in order to replace Code Division Multiple Access (CDMA), the multiple access scheme used in the 2nd and 3rd generation mobile communication systems, with Orthogonal Frequency Division Multiple Access (OFDMA) in the next generation system. 3GPP and 3GPP2 have begun standardization of evolved systems employing OFDMA. The OFDMA scheme results in a capacity increase when compared to the CDMA scheme. One reason for the capacity increase in the OFDMA scheme is that the OFDMA scheme can perform scheduling in the frequency domain (frequency domain scheduling). While the transceiver acquires capacity gain according to a time-varying channel characteristic using the CSS method, the transceiver can obtain a higher capacity gain through the use of a frequency-varying channel characteristic.
In order to increase the capacity gain using the aforementioned methods, information on the radio channel condition is required. The more accurate the radio channel condition information the greater the capacity gain. When measuring the radio channel condition based on a reference signal, the accuracy of the measurement increases as the Signal-to-Interference plus Noise Ratio (SINR) of the received reference increases. Accordingly, in order to increase the accuracy of the channel condition information, the power of the interference on the received reference signal must be reduced. Muting is one method that reduces the interference. Muting empties a time resource, a frequency resource, an antenna resource, or a code resource used by other transmitters to transmit their reference signals.
In order gain the advantages provided by muting, the transmitter should notify the receiver of the Resource Elements (REs) at which the reference signal is muted. In a 3GPP Long Term Evolution (LTE) system, for example, there are not a large number of reference signal patterns because the reference signal pattern is determined based on the Cell ID. In an LTE-Advanced (LTE-A) system, however, up to 20 reference signal patterns can be used per antenna port and multiple reference signal patterns can be muted regardless of the transmission of the reference signals.